Hops used in brewing mainly add bitterness and impart a hop flavor (e.g., taste and smell) to the final product. Hops derived from the fruit (cones) of hop plants are composed of soft resins, hard resins, hop oils, waxes, lipids, and carbohydrates. The soft resins consist of α-acids and β-acids. The soft resins and a hop oil fraction are extractable by organic solvents, or by liquid and supercritical CO2. In conventional brewing, the α-acids are converted into iso-α-acids, which are responsible for the bitterness taste. Although there is a lack of consensus as to how best to describe the character of hop flavor in beer, it is universally recognized that the hop flavor (or the kettle hop flavor) is an essential aspect of the total organoleptic impact of beer.
U.S. Ser. No. 08/838,217, now U.S. Pat. No. 5,972,411, which is incorporated by reference herein, disclosed that water soluble glycosides comprising an aromatic compound bonded to a mono-, di-, or trisaccharide may be extracted from hop or hop solids. The hop glycosides thus obtained are precursors to essences and flavorants and can be used to flavor beer. Hydrolysis of the glycosidic bond of the glycosides results in the formation of aglycons and free sugars. It is the volatile aromatic compounds that help confer flavor to beverages such as beer. Conversion of glycosides to their constituent aglycons and sugars can be achieved chemically by acid hydrolysis, enzymatically through the action of specific glycosidases, or fermentatively using whole cell biocatalysts such as yeast. The aromatic aglycons may be added to unhopped beer to impart a flavor after fermentation. The use of these kettle hop essences and flavorants provides economy, efficiency, consistency, flexibility, convenience, and quality to the brewing process.
The isolation of hop glycoside flavor precursors from hop cones as a source of flavorants used as additives to flavor beer was an improvement over the prior art. However, there remains a need for further improvements in the brewing process.
Traditionally, hops used in brewing are derived from the fruit or hop cones of hop plants, and the hop plant leaves and stems are discarded. However, the use of hop cones in brewing has certain disadvantages. The cones of hop plants contain certain hop resins, which can indirectly confer an excessively bitter taste to beer. Derivatives of hop resins are susceptible to degradation upon exposure to light, which results in the formation of compounds that impart an undesirable flavor to beer or similar beverages comprising the compounds. Therefore, beer containing hop resins is susceptible to staling or developing undesirable flavors over time, particularly if the beer is exposed to light.
There is an ongoing interest within the brewing industry to develop new methods that afford improved efficiency, cost savings, and processing advantages over prior art methods, or which yield a product having desirable characteristics, such as improved taste, reduced sensitivity to light, or an extended shelf life.
What is needed in the art is a method of isolating hop glycosides from hop plant parts that are substantially free of resins.